A. Field of the invention
The present invention relates generally to a supersonic airplane and method of operating the same, and more particularly to such an airplane and method where the propulsion system incorporates not only supersonic engines, but also a subsonic auxiliary engine or engines.
B. Background Art
A very critical factor in designing an environmentally acceptable supersonic commercial airplane is the problem of jet noise during take-off, climb, and landing. Subsonic fan jet engines having a high bypass ratio and low jet velocities are able to operate quietly. Supersonic aircraft which are generally powered by straight jet engines, operate with much higher jet exhaust velocities. High velocity jets emit high levels of low frequency jet mixing noise, which is generated outside and downstream of the engine nacelle and which therefore cannot be attenuated with internal treatment. Even if the supersonic engine is designed as a fan jet engine, the bypass ratios are generally relatively low (i.e. 0.5 to 1.0), with moderately lower jet velocities than a straight jet and the effect on alleviating jet noise is not sufficient to meet noise limits required in the future.
Over the last several decades, there have been various approaches to alleviating jet noise in supersonic airplanes. For example, there are various devices for mixing ambient air with the jet exhaust during operating modes where noise alleviation is required. Acoustic panels are used to attenuate the mixing noise generated inside this device, generally referred to as an ejector.
The ambient air utilized to mix with the jet exhaust, may be introduced through blow-in doors in the aft portion of the engine nacelle or by means of an oversized main inlet. The acoustic panels inside the ejector may either be fixed or designed to fold away in cruise.
However, proposals such as these pose various problems. For example, there is the problem of thrust losses at low speed and cruise. Further, the flat sided moving parts utilized for mixing noise suppression must be designed so that they will hold up in high temperature and high noise level environments. Also, there is the problem of incorporating thrust reversers that will operate reliably in a high temperature environment.
While these problems may be overcome through proper design and material selection, there is one remaining problem that seems to be extremely difficult to solve (if not insurmountable) using designs and concepts presently in the prior art or under consideration. This problem is that when attenuating jet noise generated by straight jet engines or low bypass ratio engines by means of ejectors, to meet today's Federal Aviation Agency (FAA) noise rules (Stage 3) or a future more stringent rule (Stage 4). The penalties resulting from the ejector (weight, nacelle drag and higher specific fuel consumption) deteriorate the airplane performance to the point where it becomes economically unattractive.
Another current approach is to provide a variable cycle engine which operates as a straight jet in cruise. At low speed a diverter valve located between the first and second compressor stages switches the first compressor stage out of the main engine cycle and into a parallel single stage fan. The variable geometry to accomplish this conversion would require a diverter valve, a stowaway inlet and a retractable fan exhaust nozzle. This poses some very significant design challenges. Also, even if these are overcome, and even though this bypass engine would have a noise problem of somewhat smaller magnitude, there may still be requirements for additional jet noise reduction.
To turn our attention to some other facets of aircraft design that are largely unrelated to the problems of noise abatement in supersonic aircraft, there have been various proposals involving aircraft engines, such as providing auxiliary engines, boost engines, various arrangements of engine inlets and exhaust, etc. A search of the patent literature has disclosed a number of these proposals, these being presented below:
U.S. Pat. No. 2,506,976 (Tharratt) shows an aircraft having jet assisting rockets mounted in the fuselage. Hinged panels are provided in a manner to enable the rockets to be carried, with these panels providing an aerodynamically clean design when in the closed position.
U.S. Pat. No. 3,084,888 (Hertel et al) discloses a VSTOL aircraft having engines which can be stowed in the fuselage and then deployed outside of the fuselage for providing vertical thrust.
U.S. Pat. No. 3,109,610 (Quenzler et al) shows a jet engine mounted within the fuselage. There is an intake position at the lower portion of the fuselage.
U.S. Pat. No. 3,134,561 (Clejan) shows a propeller-driven single-engine aircraft where there is a second emergency engine such as a pulse engine that is carried with the aircraft and deployed when needed, such as when a main engine fails.
U.S. Pat. No. 3,188,025 (Moorehead) shows a supersonic aircraft where there is a pair of aft-mounted engines on opposite sides of the fuselage. As shown on FIG. 3, these can be deployed in an upper position for takeoff and moved to a lower position for supersonic flight.
U.S. Pat. No. 3,302,907 (Wilde, et al), discloses an aircraft adapted to take-off and land vertically. There are engines which are mounted within the fuselage and which can be moved outwardly from the fuselage into an operation position.
U.S. Pat. No. 3,383,074 (Coplin) shows a VTOL aircraft where auxiliary engines can be deployed in the aircraft and then swung outwardly in a deployed position to provide vertical thrust.
U.S. Pat. No. 3,454,241 (Riemerschmid) shows a VTOL aircraft where the engines on each side of the aircraft can be swung out of the fuselage and directed downwardly for vertical thrust. The engines can also be moved to a more horizontally directed position.
U.S. Pat. No. 3,489,377 (Pearson et al) shows an aircraft having two main forward propulsion engines and an auxiliary engine which is capable of operating in two modes. First, it can simply produce thrust. Alternatively, it can produce shaft power for driving aircraft services. To produce thrust in flight, the auxiliary engine is provided with a straight exhaust. But on the ground, the exhaust is deflected to minimize noise. There is a split air inlet in the form of side of the body louvered inlet members which can be closed for flight operation.
U.S. Pat. No. 3,645,476 (Haberkorn) discloses a V/Stol where fans for the engines are stowed within the aircraft in one mode and have a position extending outwardly from the aircraft in an operating mode.
U.S. Pat. No. 4,130,258 (Fox) shows an aircraft with a retractable auxiliary engine. This auxiliary engine is normally stowed within the aircraft and then moved downwardly in a deployed position if one of the regular engines is not working properly.
U.S. Pat. No. 4,411,399 (Hapke) discloses a retractable nozzle faring system for a center boost engine. This fairing system is able to be configured aerodynamically so as to reduce the diameter of the outlet to minimize drag, and can be expanded to operate as an exhaust nozzle for a selectively operable center boost engine.
U.S. Pat. No. 4,456,204 (Hapke) discloses an aircraft where there is an engine inlet at the leading edge of a vertical stabilizer at the tail section, this leading into a center boost engine. The engine inlet can be open or closed under conditions where the center engine is operative or non-operative, respectively. The center boost engine would commonly be used during take-off, air re-fueling operations, and/or certain emergency operating conditions.
U.S. Pat. No. 4,717,095 (Cohen et al) shows a turbine driven power unit which is carried in the air frame, and then deployed into an operating position outside of the air frame when needed.
German patent 2,720,957 shows a glider having engines that are mounted in the fuselage for the glide mode and can be pivoted outwardly into the airstream for powered flight.
An article in Aircraft Engineering, dated November, 1984 at page 369 discloses the concept of using a booster engine installation where the air inlets are on opposite sides of the fuselage, and the booster engine is positioned in the aft end of the fuselage to discharge the exhaust directly rearwardly.